Heat-Shield Ablation Visualized Using Naphthalene Planar Laser-Induced Fluorescence

A combined experimental and computational study is conducted of heat-shield ablation from a scaled model of NASA's Orion Multi-Purpose Crew Vehicle in a Mach 5 wind tunnel. The ablating heat shield is made of naphthalene, which sublimates at room temperature and below, and thus is suitable for ablation studies in low-enthalpy supersonic wind tunnels. Naphthalene has the added advantage that the dispersion of the ablation products can be visualized by planar laser-induced fluorescence. Planar laser-induced fluorescence imaging of the gas-phase naphthalene reveals the distribution of the ablation products as they are transported into the heat-shield boundary layer, over the capsule shoulder, and into the separated shear layer and backshell recirculation region. High concentrations of naphthalene in the capsule separated flow region, intermittent turbulent structures on the heat-shield surface, and interesting details of the capsule shear-layer structure are observed by using the naphthalene planar laser-induced fluorescence technique. Numerical simulations of the capsule flowfield temperature and pressure fields at 0, 12, and 24deg angles of attack are then used to compute naphthalene mole fraction from the planar laser-induced fluorescence images.